Food casings, especially sausage casings, are predominantly offered in shirred form. In each case about 10 to 200 m of the casing are shirred to form a 5 to 200 cm long stick. Shirring artificial sausage skin has long been known and numerously described. On an industrial scale, shirring is performed using special machines. The casing which is delivered as roll product is taken off from the roll, inflated and pulled onto the shirring mandrel of the shirring machine. The outer diameter of the shirring mandrel determines the inner diameter of the stick to be produced. Shirring is a high stress load for the casing. Thus, too high a shirring ratio frequently leads to damage of the casing. To make the casing more supple and to reduce the mechanical friction load of the shirring systems, it is therefore customarily sprayed or wetted, immediately before shirring, or during shirring, from the inside, from the outside, or from both sides, with water, oil or an oil-in-water emulsion. This measure further prevents cracks or damage occurring at the pleats forming during shirring. The food casings thus produced are predominantly provided after the shirring process with a net-type or reinforcing packaging, so that the casings can be handled in the further processing procedure.
Cellulose-based food casings shirred in this manner have already been known for a long time. They may also be shirred in such a manner that intrinsically stable sticks are formed which are suitable for fully automatic further processing (DE-A 100 09 979). The casings are used in particular as peelable skin, for example in the production of small sausages. Cellulose skins are always shirred in the moist state. After the stick has been pulled off the shirring rod, a dimensionally stable or self-supporting shirred stick is present.
Shirred sticks made of tubular polymer-based food casings are also known. These shirred sticks, however, are generally not very stable without net-type or reinforcing packaging (see G. Effenberger, Wursthüllen-Kunstdarm [Sausage casings, artificial sausage skin], 2nd Edition [1991] pp. 58-60). In order to be able to ensure the dimensional stability of these shirred sticks, these food casings, after the shirring process, are given a reinforcing packaging. The different embodiments can comprise, e.g. shirring sleeves, tubing or net-type packaging. For transport, the shirred sticks with or without shirring sleeve are generally enclosed by a pouch or a tubular net. The shirring pleats of the polymer-based casings show a relatively high resilience, which leads to the fact that the shirred sticks without reinforcing packaging do not retain their original shape, but expand again. As a result, the mechanical intrinsic stability of the casings decreases, however, so that they can no longer be used on fully automatic stuffing apparatuses. Frequently, the skin shirred onto a sleeve is therefore fixed using limiting disks. The previously known shirred sticks, at least those without shirring sleeve, must therefore be opened either by hand or at least pushed onto the stuffing horn by hand, and then freed again from the respective reinforcing packaging which makes fully automatic operation impossible.
DE-A 196 25 094 A1 (U.S. Pat. No. 5,928,738) discloses a biaxially stretch-oriented and heatset single-layer or multilayer stick form polyamide-based packaging casing which has a shirring density of up to 1:200 at a length of the shirred stick of 40 to 100 cm, and also a method for producing such a packaging casing. The wall thickness of the packaging casing is in a range from 10 to 50 μm. Before this packaging casing is shirred, a spray solution is applied, which spray solution contains, as shirring lubricant, an emulsifier, paraffin oil or similarly active agent.
Shirred sticks having a compression ratio of up to about 150 made of an at least three-layer tubular casing are disclosed by EP-A 1 013 173. The casing has one polyamide layer each on the inside and outside. Between these layers is situated a water vapor-barrier layer, for example based on polyolefin. The casings, before shirring, are sprayed on the outside with water which can additionally contain a fungicide or preservative, and then stored in a water vapor-tight packaging, so that the water can migrate into the external polyamide layer. It is premoistening which permits the shirring with said high compression ratio.
In the older application, which was unpublished at the priority of the present application, EP-A 1 338 204, a packaging casing is disclosed which is shirred at a shirring ratio of 1:200 or higher. The high shirring ratio is achieved by the surface of the casing and that of the shirred stick together having a mean surface roughness of 0.5 to 5.0 μm. This achieves the shirred stick being able to be taken off from the shirring rod without damage. Preferably, here also, the casing is sprayed before shirring with a solution which comprises a shirring lubricant.
In the abovementioned documents, shirred sticks having high compression rates are described. Still-present resilience of the shirring pleats, the shirred sticks, however, are not intrinsically stable and are therefore customarily provided with a reinforcing packaging.